The U.S. Supreme Court has narrowly upheld the core of President Obama's health care reform requiring individuals to carry insurance.

University of Minnesota political science professor Tim Johnson joined The Daily Circuit Thursday. He said he's still parsing the 5-4 decision and how it will play out. The court based its ruling on the grounds that the mandate can be thought of as a tax. Individuals would either have to pay insurance or pay a tax, Johnson said.

"That's how the court has ultimately interpreted it: This is the Congress' power under Article 1 to say the federal government has the ability to tax for the better good -- and it seems that the court bought this argument -- if it's for the greater good that everybody pays into the health insurance system, then that as a tax, is something Congress may do," he said.

Legal and political experts said the ruling is a key moment for Chief Justice John Roberts.

Roberts is seen as a conservative justice, but he sided with the court's four liberal justices and wrote the majority decision paving the way for the law to go into effect.

Former GOP Minnesota Sen. Dave Durenberger said the decision will likely be the defining ruling for Roberts during his term on the bench.

"Roberts has done his best, as some of us expected he would, to try to take the politics out of constitutional interpretation on this law," he said.

But other Republicans, including presidential candidate Mitt Romney, responded they will fight the overhaul.

THE MEDICAID PROVISION

One way the law will increase coverage is by expanding the joint federal-state program for low-income people known as Medicaid. The expansion is expected to bring in more than $2.8 billion to Minnesota over the next few years.

Mac Baird, a primary-care physician who heads the family-medicine department at the University of Minnesota, said the ruling will benefit many people who can't currently afford health care.

"For all of us in primary care, this is a huge boost, if not in money immediately, then at least in morale," he said. "The funding streams for primary care are opening up gradually. The bill increases payments to Medicare level for those of us who serve many Medicaid patients."

Under the health care law, those patients would not have to pay for preventative services such as immunizations, Baird said.

The ruling did restrict a Medicaid provision in the federal health care overhaul, but experts said that's unlikely to make much practical difference. The high court said the expansion is constitutional as long as the federal government does not threaten to take away current Medicaid payments if a state rejects the expansion.

That leaves the possibility of uneven coverage among the states. But political science professor James Morone of Brown University said he doubts that will happen.

"Right now feds are paying 100 percent on the dollar," he said. "I think starting in 2020, they pay 90 cents of the dollar. So the state is getting 90 cents out of every dollar, they only have to match a dime for the expansion of Medicaid. Who can resist getting a buck for a dime?"

The expansion would make the most difference to low-income adults without children or disabilities.